Modeling plasma instability with electric arc discharges

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Discussion Overview

The discussion revolves around the modeling of plasma instability using electric arc discharges guided by lasers, with a focus on whether similar principles could be applied to fusion plasma. Participants explore the implications of density differences between atmospheric discharges and fusion plasmas, as well as the technical limitations of confinement in fusion systems.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants reference a paper on guiding electric arc discharges with lasers, suggesting that the stabilization observed in electric arcs might be applicable to fusion plasma.
  • Others note that the Earth's atmosphere has a much greater density than fusion plasma, questioning the relevance of the findings for magnetically confined fusion systems.
  • There is a discussion about the implications of lower density in fusion plasmas, with some participants asking if this is due to technical limits of confinement and whether higher density is generally desired.
  • One participant explains that plasma pressure is a function of particle density and temperature, and that higher density is constrained by magnetic pressure and material limits.
  • Another participant describes how laser pulses create a partially ionized column of gas with reduced density, affecting breakdown voltage and resistivity, but expresses skepticism about the applicability of this mechanism to fully ionized magnetically confined plasmas.
  • Field strength is mentioned as a limitation for magnetic confinement fusion plasmas, with some participants indicating that structural material limits are not yet a concern.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the applicability of laser-guided electric arcs to fusion plasma, and the discussion remains unresolved regarding the implications of density and confinement limitations.

Contextual Notes

Limitations include the dependence on specific definitions of plasma density and the unresolved nature of how the mechanisms discussed might translate between different plasma states.

Colin LeMahieu
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I was reading a paper recently about guiding electric arc discharges with lasers. http://loa.ensta-paristech.fr/ilm/uploads/ILM/134_Forestier_discharge_AIPAdvances_2_012151_2012.pdf

Since electric arcs are plasmas and they seem to be stabilized by lasers, could the same principle be applied to fusion plasma?
 
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Colin LeMahieu said:
I was reading a paper recently about guiding electric arc discharges with lasers. http://loa.ensta-paristech.fr/ilm/uploads/ILM/134_Forestier_discharge_AIPAdvances_2_012151_2012.pdf

Since electric arcs are plasmas and they seem to be stabilized by lasers, could the same principle be applied to fusion plasma?
With a quick read of the article, it appears the interest is inducing a more controlled atmospheric discharge, i.e., lightning, such that greater protection of electrical infrastructure is achieved. The Earth's atmosphere is many orders of magnitude greater density than a fusion plasma. It's not clear the advantage of this process for magnetically confined fusion systems. Perhaps the_wolfman can provide some insight.
 
Interesting. I could see how lower density could affect results. Is the lower density because of technical limits to confinement? Higher density would generally be desired if possible, right?
 
Colin LeMahieu said:
Interesting. I could see how lower density could affect results. Is the lower density because of technical limits to confinement? Higher density would generally be desired if possible, right?
The pressure of the plasma is a function of particle density, n, and the temperature, T, by virtue of P = nkT, where k is the Boltzmann constant.

http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/idegas.html#c1

The plasma pressure is limited by the magnetic pressure and the structural materials confining the plasma. Higher density would be desirable, but we are constrained by the limits on materials.
 
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Colin LeMahieu said:
I was reading a paper recently about guiding electric arc discharges with lasers. http://loa.ensta-paristech.fr/ilm/uploads/ILM/134_Forestier_discharge_AIPAdvances_2_012151_2012.pdf

Since electric arcs are plasmas and they seem to be stabilized by lasers, could the same principle be applied to fusion plasma?

The laser pulse creates a partially ionized of column of gas that has a reduced density. These two effects reduce the breakdown voltage and resistivity is the column. Current takes the path of least resistance, so the laser pulse is creating a preferred path for the arc to follow.

Magnetically confined plasmas are usually completely ionized. So its hard to imagine where this mechanism would be applicable except maybe during start up.

It is interesting thato the arcs have such a well defined cylindrical shape.
 
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As far as I know, field strength is a limitation with magnetic confinement fusion plasmas, but not structural limits of materials, not yet.
 

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